A typical approach to providing beverage or other containers (such as, commonly, 12 ounce to 32 ounce pop or beer containers), involves a two piece construction procedure involving forming a body piece which contains a (typically cylindrical) sidewall and a bottom, all formed from a single piece of metal, typically aluminum, and a second top or cover piece joined to the rim of the body piece, e.g. by a seaming or curling operation. An important consideration in designing and fabricating such containers involves providing a desirable balance between minimizing material requirements (such as providing relatively thin-gauge metal) while achieving a container that will maintain its integrity and/or form, despite shipping and handling impacts or forces and despite impact or forces arising from dropping containers and the like. Moreover, it is typically desired to provide containers which maintain integrity and/or form even when contents are under pressure (e.g. a rising from carbonated or otherwise gas-pressured contents and/or arising from high temperatures, including, in some cases, pasteurization temperatures).
Theoretical analysis and practical experience both indicate that it can be advantageous to provide a bottom shape which is substantially convex (when viewed from the outside). Theoretical analysis indicates that a bottom shape which is in the form of a hemispherical section, outwardly convex, provides substantially the greatest strength, especially for pressurized contents.
A convex bottom shape can also be of assistance, in reducing materials costs, by providing additional interior volume (compared, e.g., to a concave bottom shape), in some cases making it possible to reduce the sidewall height of a container (and thus reduce materials costs) while retaining the same interior volume available for container contents. Nevertheless, an outwardly convex or hemispherical bottom shape is not typically provided in mass-produced metal beverage (and other) containers. A more common bottom configuration for a beverage container involves a bottom panel which is concave (viewed from the outside) over the majority of the bottom surface (e.g. except for formation of a support rim), such as those described and depicted in U.S. Pat. No. 5,836,473.
As the container industry has developed, there has been an increase in factors favoring further reduction of materials costs without substantially sacrificing strength. Accordingly, it would be useful to provide a design which can take advantage of the strength characteristics associated with a hemispherical or otherwise outwardly convex bottom shape.
A number of factors place constraints on container shape and design. For containers which are to be mass produced, such as typical pop, beer or similar containers, the design must be compatible with high-speed manufacturing and is preferably achieved while making only minimum modifications to fabrication lines. Such manufactureability considerations have made it difficult or infeasible to implement at least some convex-bottom shapes, especially when container bodies are fabricated from aluminum. Without wishing to be bound by any theory, it is believed that this is at least partially because of the relatively limited ductility or stretchability of aluminum, e.g. compared to steel or other potential container metals. Many potential container bottom shapes with convex proportions are believed to be substantially unmanufactureable, e.g. in aluminum (in a mass production setting) because the limited ductility of aluminum leads to rupture, buckling or folding during container body formation processes. In many instances, while it might be theoretically possible to form aluminum into certain desired shapes, such formation would require the addition of equipment or would require a slowdown of production of a magnitude making it infeasible or undesirable in a mass production environment. Because of the properties of aluminum, it is, in general, not feasible to conclude that a shape that can be formed in another material, such as another metal, or a plastic, can be feasibly formed in aluminum, especially in a mass-production fashion. Accordingly, it would be useful to provide a configuration which can take advantage of the strength characteristics available from an (at least partially) convex or hemispherical bottom shape, but which is feasible for production, especially for aluminum container bodies, in a high-throughput, mass production environment, preferably without requiring substantial additional equipment or fabrication stations and/or without requiring a slowdown of production rates.
In addition to design constraints imposed by manufactureability, a number of other factors are profitably considered, including stackability and conveyability. Stackability refers to the ability to vertically stack one can on top of another, preferably to achieve multiple-can heights of a stack. Typically, stackability involves designing a container bottom in conjunction with the design of the container top, e.g. to achieve desired nesting and clearance characteristics and generally to achieve desired stackability. Conveyability refers to the ability to slide or otherwise convey a (typically vertically-oriented) container along a tray or trough surface, roller surface, belt surface and the like, while avoiding tipping or "stumbling" of containers during conveyance. Accordingly, it would be useful to provide a container which may take advantage of increases in strength associated with a container bottom having a (at least partially) convex or hemispherical shape while providing desired stackability and conveyability characteristics.
Another design factor involves the ability of a container to accommodate changes in differential pressure, such as pressure arising from carbonation or other pressurization of contents, pressure arising from changes in temperature, such as temperatures ordinarily encountered during shipment storage and the like and/or processing temperatures, including, in some cases, pasteurization processes. In some situations, differential pressure changes can arise from changes in the external environment such as conveyance or use of containers in aircraft or other reduced-pressure environments. Accordingly, it would be useful to provide a container bottom design which could take advantage of the increased strength associated with providing a container bottom with an (at least partially) convex shape or hemispherical shape while accommodating reasonably anticipated changes in differential pressure (i.e. pressure differences between internal pressure and external pressure).